1. Field of the Invention
The invention relates to a process for the preparation of chlorinated pyrimidines, chloro alkyl-substituted in the 5-position, of the general formula ##STR4## wherein
R.sub.1 represents fluorine, chlorine, bromine, trichloromethyl, phenyl or hydrogen or a second chlorinated pyrimidine ring substituted in the 5-position,
R.sub.2 represents hydrogen, fluorine, chlorine, bromine, alkyl with 1 to 6 C atoms, phenyl, nitrophenyl or chlorophenyl,
R.sub.3 represents hydrogen, fluorine, bromine or chlorine and
R.sub.4 represents fluorine, chlorine, bromine, trichloromethyl or hydrogen.
2. Discussion of Prior Art
It is already known that chlorinated pyrimidines can be prepared by reacting acetonitriles with chlorinated isocyanide dichlorides (DT-OS (German Published Specification) No. 1,670,854). In order to be able to prepare chlorinated pyrimidines with a chlorine-containing alkyl group in the 5-position of the pyrimidine ring by this process, it is necessary to use propionitriles which have a chlorine atom in the .beta.-position and are unsubstituted in the .alpha.-position as the starting materials. In most cases, the .beta.-chloropropionitriles required as the starting material must be prepared from the .alpha.,.beta.-unsaturated nitriles. Thus, .beta.-chloropropionitrile is prepared from acrylonitrile, but undesired by-products are formed.
According to the present invention there is provided a process for the preparation of the chlorinated pyrimidines, chloro-alkyl substituted in the 5-position, of the formula I, in which halogeno-azaalkenes of the general formula II ##STR5## wherein
R.sub.1 can represent fluorine, chlorine, bromine, trichloromethyl, phenyl, hydrogen or --CCl.sub.2 --N.dbd.CCl.sub.2,
R.sub.4 can represent fluorine, chlorine, bromine or trichloromethyl and
R.sub.5 can represent fluorine, chlorine, bromine or hydrogen,
are reacted with .alpha.,.beta.-unsaturated nitriles of the general formula III ##STR6## wherein
R.sub.2 represents hydrogen, chlorine, fluorine, alkyl with 1 to 6 C atoms, cycloalkyl, phenyl, nitrophenyl or chlorophenol,
R.sub.3 represents hydrogen, fluorine or chlorine and
R.sub.6 represents hydrogen, fluorine, chlorine or bromine.
The starting components (II) and (III) are reacted with one another in accordance with the process according to the invention in approximately stoichiometric proportions or with an excess of one or other of the components. If a bis-(isocyanide dihalide) is employed as the starting component (II), the nitrile component is employed in approximately twice the stoichiometric proportion.
Compounds of the formula (II) which are suitable for the process are, for example, chloromethyl isocyanide dichloride, trichloromethyl isocyanide dichloride, pentachloroethyl isocyanide dichloride, pentachloroethyl isocyanide dichloride, phenyl-dichloromethyl isocyanide dichloride and perchloro-2,5-diazahexa-1,5-diene; perchloro-3,6-diazaocta-2,6-diene; and 1,1,3,4,4,4-hexachloro-2-azabut-1-ene and fluoro-dichloromethyl isocyanide dichloride.
Unsaturated nitriles of the formula (III) which are suitable for the process are, for example, acrylonitrile, methacrylonitrile, crotononitrile, cinnamic acid nitrile, 3-nitrocinnamic acid nitrile, 3-chlorocinnamic acid nitrile, .alpha.-chloroacrylonitrile, .alpha.,.beta.-dichloroacrylonitrile, trichloroacrylonitrile, fumaric acid nitrile and .alpha.-bromoacrylonitrile.
The process according to the invention can be carried out in the presence or absence of inert solvents or diluents at temperatures from 20.degree.-350.degree. C. The reaction is preferably carried out at 100.degree.-220.degree. C.
The reaction can be carried out under normal pressure and under autogenous pressure and optionally in the gas phase, preferably a pressure up to 20 atm is suitable.
In general, it is advantageous in the process according to the invention to heat the starting components together in stoichiometric amounts or to use one of the starting components or the end product as a solvent. It can be advantageous to initially heat the component used as a solvent to the reaction temperature and then to introduce the second component.
Aliphatic, cycloaliphatic and aromatic hydrocarbons with up to 10 C atoms can be used as the solvent, it being possible for the hydrocarbons mentioned to be optionally substituted by halogens and/or nitro groups.
Examples which may be mentioned are: methylene chloride, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, trichloroethylene, 1,2-dichloropropane, trichloropropane, sulpholane, chlorobenzene, dichlorobenzene, nitrobenzene or one of the reactants in excess. Preferred solvents are chlorinated hydrocarbons or sulphones.
The reaction can be accelerated by acid or basic catalysts. The catalysts can be applied to an inert support material. Suitable acid catalysts are, for example, Lewis acids, such as iron-III chloride, aluminium chloride, zinc chloride, copper-I chloride, palladium chloride, boron trifluoride, antimony trichloride and titanium tetrachloride. Examples of suitable basic catalysts which may be mentioned are: triethylamine, pyridine and dimethylformamide.
The catalysts are generally added in an amount of 0.001 to 10% by weight of one of the starting components, or the components are passed over the catalyst, which has been applied to a solid support. A catalyst amount of 0.1 to 5% by weight has proved particularly advantageous.
The reaction can be illustrated with the aid of the following equation: ##STR7##
Preferred processes according to the present invention comprise reacting acrylonitrile with a perchlorinated alkyl isocyanide dichloride.
According to a particularly preferred embodiment, trichloromethyl isocyanide dichloride is reacted with acrylonitrile, preferably in the temperature range from 100.degree. to 350.degree. C., in the presence of catalytic amounts of a Lewis acid catalyst, 2,4,6-trichloro-5-chloromethyl-pyrimidine being obtained in very good yields.
The process according to the invention is therefore particularly suitable for the preparation of chlorinated pyrimidines carrying a substituted methyl group in the 5-position, in particular 2,4,6-trichloro-5-chloromethylpyrimidine. In this respect, the course of the reaction is surprising since in general cyclisation reactions with .alpha.,.beta.-unsaturated nitriles take place with the inclusion of the .beta.-C atom in the ring formed.
2,4,6-Trichloro-5-chloromethylpyrimidine is a known intermediate product. The volume of the products of the process are new intermediate products which are suitable, for example, for the preparation of reactive dyestuffs. Compounds of formula (I), except those in which R.sub.1, R.sub.3 and R.sub.4 denote chlorine and R.sub.2 denotes methyl, thus also form part of the present invention.